What should the installation of supply lines and fittings for all fixtures prevent?

The installation of supply lines and fittings for all fixtures should primarily prevent backflow. Backflow occurs when water flows in the opposite direction from its intended path, potentially leading to contamination of the potable water supply. To ensure safe drinking water, the plumbing system must include proper backflow prevention devices and correct installation techniques that maintain the desired flow direction. This helps protect public health by preventing contaminants from entering the clean water supply, a critical aspect of plumbing standards and regulations.

While preventing clogs, flow rate issues, and leaks is certainly important in plumbing design, the main goal concerning supply lines and fittings is focused on avoiding backflow, as it poses the greatest risk to water quality in the system.